During the conduct of operations in a borehole a tool or a tubular string can get stuck and needs to be worked free. Tools that wash over the stuck tool that is also known as a fish are called overshots. These tools have a low end opening that accepts the upper end of the stuck fish. There is a gripping device in the overshot to engage the fish. One type of such gripping device is a thread form that digs into the fish as the overshot is turned to the right. As the string supporting the overshot is turned to the right with weight set down it digs a thread pattern into the fish so that when the rotation is stopped and the set down force is removed in favor of a pickup force, the fish is then subjected to the pickup force and will hopefully release so that it can be brought out of the wellbore.
In the past, overshots had a fixed seal mounted in the receptacle for the fish with the idea that the seal would engage the outside diameter of the fish and make a seal. One such tool is the High Pressure Packoff sold by Baker Oil Tools under the Product Family number H11059. The problems arose when the gap to the fish was sufficient that the internal seal in the overshot could not effectively seal against the body of the fish to deliver pumped pressure into the fish. This could happen for a variety of reasons. One reason is simply the availability at the location of a choice of overshots that have a variety of seal sizes and the resulting dimensional mismatch between the available seal in the overshot and the exterior dimensions of the fish. Another issue could be the condition of the exterior surface of the fish at the top where the overshot drops down on the fish. The exterior surface of the fish could have scale or burrs or could be out of a rounded shape, to cite a few examples.
One attempt to seal a fish in an overshot is shown in U.S. Pat. No. 4,052,861 where an inflatable pushes out collet heads with grip surfaces on a side facing the fish to try to hold the fish. While this design looks like it might work on paper the reality is that a pulling force on the overshot will distort the inflatable until one end of the inflatable will come loose from its seal against the inner housing wall. While the inflatable in this design is intended to push the collets to grip and seal where it contracts the fish the inflatable design is very weak structurally and lends no meaningful support to the collet heads under pulling loads so that a release from the fish is likely. A separate control or fill line is also needed to inflate which takes up space and precludes use of the tool in smaller boreholes.
The present invention offers an articulated seal that can handle a range of shapes and sizes at the top of the fish and allows for a clearance for fast engagement and a subsequent actuation of the seal to close a wide range of gaps with a pressure seal that will allow pumping into the fish to actuate a pressure responsive component on the fish or that will allow circulation or reverse circulation through the fish. In the preferred embodiment a swelling material that is responsive to hydrocarbons or water or both can be used as the seal. Mechanically or hydraulically actuated seals are also contemplated. Those skilled in the art will have a better understanding of the invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.